(1) Field of the Invention
The present invention is related to an artificial force feel generating device for generation of an artificial feeling of force on an inceptor of a vehicle control system. The invention is further related to an aircraft with a vehicle control system that comprises an artificial force feel generating device for generation of an artificial feeling of force on an inceptor of said vehicle control system.
(2) Description of Related Art
Artificial force feel generating devices are frequently used in vehicles that are controllable in a flowing medium, such as air or water, and that are provided with servo-assisted control units that are controlled by suitable associated inceptors, such as control sticks, control columns, sidesticks, pedals, steering wheels and so on. For instance, artificial force feel generating devices are used in aircrafts, such as airplanes and helicopters, or in watercrafts, such as ships, boat, hovercrafts and submarines.
By way of example, an artificial force feel generating device that is used in an aircraft is usually adapted for generating artificial breakout forces for an inceptor of a given servo-assisted control unit, such as a rudder, and additional optional artificial force gradients for convenient control of this inceptor by the pilot. The artificial breakout forces and additional optional artificial force gradients are forces that need to be overcome by the pilot when moving the inceptor from a predetermined neutral position into a respective operating position desired by the pilot.
The predetermined neutral position is a position of the inceptor that corresponds to a preferred motion direction of the aircraft and that is generally characterized in that in it no forces act on the inceptor. In other words, no forces need to be applied onto the inceptor in operation for keeping it in its neutral position.
A reel, e.g. centering and/or anchoring, feeling of the artificial breakout forces and the additional optional artificial force gradients usually becomes noticeable to the pilot of the aircraft when the inceptor passes a so-called trim point on its travel from the neutral position to the respective desired operating position. This trim point is slidable, i.e. adjustable within a defined control range by means of a trim coupling and/or a trim motor. However, in order to enable the pilot to sensitively control the aircraft, the artificial forces generated by the artificial force feel generating device, i.e. the artificial breakout forces and the additional optional artificial force gradients, should be relatively moderate.
If an automatic flight control system (AFCS) is used with the aircraft, the artificial breakout forces are usually used to support a respective input of AFCS actuator signals onto the inceptor. The forces that can be applied to the inceptor by such an AFCS are, thus, limited by the artificial breakout forces.
In operation of the aircraft, any overcoming of the artificial breakout force or movement in the region of the additional optional artificial force gradients is generally assessed by the AFCS as being an intended intervention by the pilot and, thus, results in temporary degradation of the AFCS operating mode in order to prevent the pilot and the AFCS from working against each other. Depending on the type of aircraft and a given flight situation, degradation of the AFCS operating mode can take place to a different extent.
For example, complete degradation of the AFCS operating mode is imaginable so that control of the aircraft takes place exclusively as a result of the manual control intervention of the pilot. However, partial degradation is also possible, in which the aircraft continues to be stabilized by the AFCS, while the pilot handles the trajectory control input via manual control intervention, for example the flight direction or altitude.
A complete degradation provides the pilot with a direct intervention option in the control and in unequivocal automatic degradation of the AFCS operating mode in favor of manual control by the pilot. This design allows preventing situations in which the AFCS and the pilot unintentionally work against each other, which might otherwise lead to critical flight situations. However, such a direct intervention option for the pilot requires moderate breakout forces in order to make comfortable manual control possible.
The entire breakout forces are composed of the component friction in the control system and the additional artificial breakout forces to support the AFCS operating mode. Since the entire breakout forces are to be overcome by the pilot, there is a disadvantage in that in the case of substantial undesirable component friction it is only possible to select slight artificial breakout forces to support the AFCS operating mode and, consequently, this results in high sensitivity of the system to any unintended intervention by the pilot. However, in this case an unintended bumping against the inceptor, or an unintended fixing of the inceptor by the pilot, may result in complete degradation of the AFCS operating mode, without this being intended and/or noticed by the pilot. Furthermore, as has already been mentioned, slight, i.e. small artificial breakout forces also limit the forces that can be exerted on the inceptor in the AFCS operating mode.
In contrast thereto, a partial degradation allows the AFCS operating mode to remain active until it is intentionally degraded by the pilot with the use of a switch or a contact sensor on the inceptor. This design results in improved robustness to unintended pilot intervention, but the absence of automatic degradation during pilot intervention may lead to critical flight situations, as described above. Activating the switch or the contact sensor on the inceptor generally results in decoupling of an underlying trim coupling, as a result of which a trim motor, via which the AFCS operating mode intervenes, is decoupled from the inceptor. Such decoupling generally also results in a reduction in the breakout forces, e.g. by partial or complete decoupling of the artificial breakout forces.
The pilot is then in a position to carry out manual control of the aircraft with reduced breakout forces. Furthermore, it is possible to use increased artificial breakout forces in the AFCS operating mode and, thus, to increase the range of forces for the AFCS operating mode, because manual control by the pilot takes place with partial or complete decoupling of these artificial breakout forces. However, decoupling of the trim motor generally also results in the loss of the original trim point, which is often perceived by the pilot as being disagreeable, as after termination of manual intervention the trim point must be newly adjusted.
Furthermore, combinations of the above described designs exist, in which degradation of the AFCS operating mode can take place either by way of direct intervention by the pilot or by overcoming the entire breakout forces and by activation of a switch or of a contact sensor on the inceptor. These combinations are, however, also associated with the already mentioned disadvantages in that the artificial breakout forces that are available to the AFCS operating mode for acting on the inceptor need to be moderate in order to make manual intervention by the pilot possible, and in that during decoupling of the trim coupling the trim point is lost.
Exemplary artificial force feel generating devices are e.g. described by the documents EP 2 266 878 B1, EP 2 311 729 A1 and US 2010/0123045 A1. In these exemplary artificial force feel generating devices, a force applied to a corresponding inceptor by the pilot is measured by an external force or pressure sensor for controlling the devices on the basis of the measured force.
However, in all of the above described conventional artificial force feel generating devices, electric motors are immediately connected to corresponding spring units for directly loading these spring units such that they provide an associated servo-assisted control unit with a generated artificial feeling of force. Thus, in case of loss of electrical power or in case of loss of the electric motors as such, the generated artificial feeling of force will also be lost.
A further major inconvenient of the conventional artificial force feel generating devices consists in their inadequacy for implementing flight domain limitation and limit indication for the purpose of carefree handling of an aircraft and, in particular, of a rotary wing aircraft such as a helicopter. More specifically, helicopters, as well as aircrafts in general, are subject to flight domain limitations, such as thermal and/or mechanical engine limitations, gearbox torque limitations, structural load limitations, performance limitations and stability limitations.
Other flight domain limitations are e.g. related to preferred flight paths or so-called “tunnels in the sky”, i.e. avoidance of man-made obstacles, specific terrains or traffic. Furthermore, in helicopters having a bearingless main rotor, a respective mast bending moment of a given rotor mast of the main rotor in operation defines an important structural limitation that pilots have to consider during flight for not damaging the helicopter. If any one of these limitations is exceeded, an unscheduled and expensive maintenance action can be required.
Usually, flight domain limitation is implemented in aircrafts in the framework of so-called fly-by-wire systems, where there is no direct mechanical connection between a given inceptor and respectively controlled flight control surfaces. In other words, currently there is no flight domain limitation implemented by means of kinematics of mechanical flight controls. Instead, only specific limitations are monitored by dedicated devices. For instance, the mast bending moment is visualized by a one- or two-dimensional optical display and/or a so-called first limit indication is provided by an optical instrument that depicts a current status of engine and gearbox in comparison to predetermined limitations of, e.g., temperature, torque and/or speed. Furthermore, the above described conventional artificial force feel generating devices are used to provide tactile feedback to the pilots.
However, all of these measures only result in an increased workload of the pilot who must look at the various instruments during flight and interpret a respective behavior of the inceptor. This increased workload may result in intended or unintended damaging actions of the pilot that may lead, e.g., to an excessive mast bending moment, an excessive engine temperature or an excessive gearbox torque, which would require the above mentioned unscheduled maintenance action or reduced intervals for scheduled maintenance. Furthermore, the required dedicated devices are difficult to retrofit as generally flight control kinematics may not be compatible.